Union Pacific 4017, or UP 4017, is a four-cylinder articulated 4-8-8-4 Big Boy-type steam locomotive owned by Union Pacific Railroad. It was Built by Alco in 1941 along with the other Big Boy locomotives to fix problems with the preceding 4-6-6-4 Challenger class locomotives.

It ran in service hauling Freight Trains until July 21, 1959, when it was retired along with the other Big Boy Locomotives.

It is now a Static Display at the National Railroad Museum.


No. 4017 is one of eight surviving Big Boy.

The locomotive was one of the last Big Boys to undergo heavy repairs at Union Pacific's Cheyenne, WY, workshops in July 1959.

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